Soft x-ray pulses of submicrosecond duration are needed to test materials and components of pulsed fusion reactions. Techniques presently employed to generate such pulses are (a) electron diode guns bombarding a heavy metal target, (b) underground fusion devices and (c) dense focus with high Z-material electrode tips which erode during the pulse. Electron diode guns at the required x-ray energies of fractional MeV are very inefficient because the conversion efficiency of electron beam energy into Bremsstrahlung decreases superlinearly with the decrease of electron energy for a given target anode, a fact which is well known to the designers of flash x-ray tubes. In addition, at low electron energies of fractional MeV, the space charge of electron beam is not cancelled by relativistic effects and limits severely the maximum current density of the electron beam available at the target anode. Furthermore, the electric fields of the cathode are usually not sufficient to obtain a copious electron emission by the field effect and therefore the thermionic cathodes must be employed which intrinsically yield a much lower electron emission current density than field emitters. Present electron beam-Bremsstrahlung flash generators of minimum useful x-ray fluence therefore employ electron beams in the several MeV range. They generate x-ray flashes of spectral distribution which contains most of the photon energy in the hard x-ray spectral range. Because the x-ray penetration depth decreases superlinearly with the photon energy, the deposited x-ray energy density in test materials and components is substantially different for soft and hard x-ray flashes of identical fluence at the source. Therefore, pass-fail conclusions of tests on materials, components and devices performed with many MeV energy electron beam x-ray flash generators are not directly scalable to predict the performance under a soft x-ray flash. Underground fusion flash tests suffer from the intrinsic inability to separate by the time-of-flight method the various components of radiations and expansion waves generated during the test. Therefore, various radiation and blast wave effects cannot be readily differentiated and only the cumulative, gross effects are observed. Thus, the materials designer is handicapped in separating the individual contributions from each damaging radiation.
The plasma focus alone can also be used as a soft x-ray flash generator by altering the electrode design and configuration such as to increase the evaporation and erosion of certain portions of the electrodes. Because only the energy stored in the plasma focus can be used for soft x-ray production, the fluence of x-ray flash is limited. In addition, a full control of erosion of the electrodes cannot be achieved in this case. Therefore, the intensity and the spectral distribution of x-ray flashes varies from one firing to another.
Therefore, it is an object of this invention to overcome deficiencies and eliminate or substantially reduce problems encountered in producing soft x-rays.
Another object of this invention is to provide a x-ray generator that utilizes the interaction of an electron beam with a plasma to provide an additive effect to the plasma to cause an increase in the production of soft x-rays when the plasma has been seeded with high Z-material.
Still another object of this invention is to arrange and control the interaction of the plasma with the electron beam such that the electron beam energy is focused onto the very small volume of dense hot plasma of the plasma generator so as to obtain the additive effect.
A further object of this invention is to focus the electrons from the electron beam source utilizing a sealed pinch tube.
Still a further object of this invention is to affect the orbits of the electrons from the electron source as they approach the dense hot plasma by the effects from the fields of the sealed pinch tube.